Communication systems utilizing Radio Frequency (RF) signals often convert the received signal into an in-phase (I) component and a quadrature (Q) component. A mismatch in these electrical components in the signal channels causes I/Q imbalances in the received signal. The I/Q imbalances, such as amplitude imbalance and phase imbalance, are frequency-dependent and highly unpredictable. For communication systems where the received signal is converted into its constituent baseband I/Q components (eg: Direct Conversion Receivers), the I/Q mismatch and intrinsic Local Oscillator (LO) self-mixing will introduce a Direct Current (DC) offset error in base-band I/Q signals. These errors degrade the signal quality, hence detection and correction of these errors becomes necessary.
Various methods exist in the art for correcting said I/Q imbalances and DC offset errors. In one method, the I/Q phase and amplitude balance is compensated by using synchronous calibration regions embedded in packet data signals. The amplitude ratio I/Q is calculated directly, and the phase balance is checked for orthogonality in relation to the expected 90 degrees. In another method, the I/Q phase and amplitude imbalance is corrected in real time by using pilot signals that are embedded in the RF carrier. In yet another method, a differentiate-cross-multiply demodulator strategy is used, which utilizes two correction factors. One of the correction factors is scaled as a quotient of the divide operation to minimize distortion.
The methods described above suffer from one or more of the following limitations. First, the methods, while receiving the signals, are not able to eliminate amplitude imbalance, phase imbalance and DC offset errors in real time. Second, the methods are not immune to a highly dynamic RF and parametric environment. Third, some of the methods require pilot signals and cannot operate piece-wise continuously on the actual signal.
Accordingly, there is a need for an improved I/Q imbalance and DC offset correction.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.